BACKGROUND OF THE INVENTION
[0001] The present invention relates to an image reading apparatus, an image processing
apparatus, and a method therefor and, more particularly, to an image reading apparatus,
an image processing apparatus, and a method therefor using a linear image sensor for
performing an intra-pixel transfer/read-out operation.
[0002] Conventionally, as a color image reading apparatus using a linear image sensor, an
apparatus with the arrangement shown in Fig. 1 is known.
[0003] In the color image reading apparatus shown in Fig. 1, an original 212 on an original
table glass 211 is illuminated with light using an illumination light source 210 and
a reflector 209, and light reflected by the original is imaged on the light-receiving
surface of a CCD (color linear image sensor) 201 via a first mirror 208, a second
mirror 205, a third mirror 206, and a lens 202. When a portion surrounded by a broken
line 207 in Fig. 1 is moved at a velocity V in the direction of an arrow in Fig. 1,
and a portion surrounded by a broken line 203 is moved at a velocity V/2 in the direction
of an arrow in Fig. 1, the entire image on the original 212 can be read by the CCD
201.
[0004] Fig. 2 shows the arrangement of the CCD linear image sensor 201 used in the conventional
color image reading apparatus.
[0005] Referring to Fig. 2, reference numerals 301, 302, and 303 denote light-receiving
units respectively having R (red), G (green), and B (blue) color filters. In each
light-receiving unit, diodes for converting photons into charges (electrons in this
case) are arranged in units of pixels. Charges generated by light reception for a
predetermined period of time are respectively transferred (shifted) to CCD transfer
units (charge transfer units) 304, 306, and 308 for ODD pixels and CCD transfer units
(charge transfer units) 305, 307, and 309 for EVEN pixels. The charges transferred
(shifted) to the CCD transfer units are sequentially transferred in a predetermined
direction in the corresponding CCD transfer units while the light-receiving units
perform light-receiving and charge storage operations for the next line, and are sequentially
converted into voltage signals by amplifiers 310 to 316. Then, these voltage signals
are output.
[0006] However, as shown in Fig. 2, in the conventional color linear image sensor, since
the CCD transfer units for charge transfer are arranged between adjacent ones of the
R, G, and B light-receiving units, the interval between the R and G light-receiving
units and the interval between the G and B light-receiving units shown in Fig. 2 must
be set to be large.
[0007] When the interval between adjacent light-receiving unit increases, a memory for correcting
the reading Positions of R, G, and B signals is required when read R, G, and B signals
are subjected to color correction processing such as masking calculations. In this
case, as the intervals of the R, G, and B light-receiving unit become larger, the
required memory capacity undesirably increases.
[0008] Recently, a structure wherein CCD transfer units are disposed to sandwich light-receiving
units of different colors therebetween in place of being disposed adjacent to the
corresponding light-receiving units is proposed (Japanese Patent Application Nos.
6-187157 and 6-197075).
[0009] Fig. 3 shows the arrangement wherein the CCD transfer units are disposed to sandwich
the light-receiving units of different colors therebetween. In this case, since the
CCD transfer units need not be disposed between the adjacent light-receiving units
of the respective colors, the interval between the adjacent ones of the R, G, and
B light-receiving units can be greatly reduced and the required memory capacity can
also be reduced as compared to a conventional sensor.
[0010] However, received and stored charges must be transferred (shifted) to the CCD transfer
units via the light-receiving units (pixels) of different colors. When so-called intra-pixel
transfer is performed, since each light-receiving unit is receiving light reflected
by an original image while charges are passing through the light-receiving units of
different colors, color mixing may occur upon transfer.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in consideration of the above situation, and
has as a concern to provide an image reading apparatus, an image processing apparatus,
and a method therefor, which can eliminate color mixing even when a linear image sensor
in which charge transfer units are disposed to sandwich light-receiving units of different
colors therebetween is used.
[0012] According to one embodiment of the present invention, an image pickup apparatus for
reading a color image by irradiating light onto an object, and photoelectrically converting
light from the object, comprises: a linear image sensor which comprises a plurality
of light-receiving portions corresponding to light components of a plurality of colors,
and transfer units which are arranged on two sides of the plurality of light-receiving
portions and transfer charges from the light-receiving portions, a charge stored in
the light-receiving portion of at least one color being transferred to the transfer
unit via the light-receiving portion of another color; and calculation means for performing
a calculation of the charge transferred via the light-receiving portion of the other
color.
[0013] An image reading method according to the present invention is characterized by the
following arrangement.
[0014] More specifically, an image pickup method for reading a color image by irradiating
light onto an object, and photoelectrically converting light from the object, comprises
the steps of: preparing a linear image sensor which comprises a plurality of light-receiving
portions corresponding to light components of a plurality of colors, and transfer
units which are arranged on two sides of the plurality of light-receiving portions
and transfer charges from the light-receiving portions, a charge stored in the light-receiving
portion of at least one color being transferred to the transfer unit via the light-receiving
portion of another color; and performing a calculation of the charge transferred via
the light-receiving portion of the other color.
[0015] An image pickup apparatus according to the present invention is characterized by
the following arrangement.
[0016] More specifically, an image pickup apparatus comprises: a first light-receiving sensor;
a second light-receiving sensor; transfer means, arranged on a side near the second
light-receiving sensor and opposite to the first light-receiving sensor, for reading
out charges of the first and second light-receiving sensors; control means for reading
out a charge signal of the second light-receiving sensor via the transfer means, and
for transferring a charge signal of the first light-receiving sensor toward the transfer
means via the second light-receiving sensor, and then reading out the charge signal
via the transfer means; and subtraction means for subtracting the signals of the first
and second light-receiving sensors read out via the transfer means.
[0017] An image processing apparatus according to the first aspect of the present invention
is characterized by the following arrangement.
[0018] More specifically, an image processing apparatus comprises: reading means for reading
a color image by an intra-pixel transfer method; acquisition means for acquiring color
mixing information between different color signals from signals obtained by reading
a standard original by driving the reading means in at least two different modes;
and correction means for correcting color mixing of image data read by the reading
means on the basis of the color mixing information acquired by the acquisition means.
[0019] An image processing apparatus according to the second aspect of the present invention
is characterized by the following arrangement.
[0020] More specifically, an image processing apparatus comprises: reading means for reading
a color image by an intra-pixel transfer method; acquisition means for acquiring color
mixing information from a first color component to a second color component signal
on the basis of a signal obtained by reading a standard original by the reading means;
and correction means for correcting color mixing of image data read by the reading
means on the basis of the color mixing information acquired by the acquisition means.
[0021] An image processing method according to the first aspect of the present invention
is characterized by the following arrangement.
[0022] More specifically, an image processing method comprises: the acquisition step of
acquiring color mixing information between different color signals from signals obtained
by reading a standard original by driving reading means for reading a color image
by an intra-pixel transfer method in at least two different modes; and the correction
step of correcting color mixing of image data read by the reading means on the basis
of the color mixing information acquired in the acquisition step.
[0023] An image processing method according to the second aspect of the present invention
is characterized by the following arrangement.
[0024] More specifically, an image processing method comprises: the acquisition step of
acquiring color mixing information from a first color component to a second color
component signal on the basis of a signal obtained by reading a standard original
by reading means for reading a color image by an intra-pixel transfer method; and
the correction step of correcting color mixing of image data read by the reading means
on the basis of the color mixing information acquired in the acquisition step.
[0025] Other features and advantages besides those discussed above shall be apparent to
those skilled in the art from the description of a preferred embodiment of the invention
which follows. In the description, reference is made to accompanying drawings, which
form a part hereof, and which illustrate an example of the invention. Such example,
however, is not exhaustive of the various embodiments of the invention, and therefore
reference is made to the claims which follow the description for determining the scope
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
Fig. 1 is a view for explaining the optical system of a conventional color image reading
apparatus;
Fig. 2 is a view showing the arrangement of a CCD linear image sensor of the conventional
color image reading apparatus;
Fig. 3 is a view showing another arrangement of a CCD linear image sensor of the conventional
color image reading apparatus;
Fig. 4 is a view showing the arrangement of a CCD linear image sensor of an image
reading apparatus as the basis of the present invention;
Fig. 5 is a view showing the arrangement of the image reading apparatus according
to the first embodiment of the present invention;
Fig. 6 is a view showing the movement of charges in intra-pixel transfer according
to the present invention;
Fig. 7 is a view for explaining an image reading operation according to the second
embodiment of the present invention;
Fig. 8 is a view showing the arrangement of an image reading apparatus according to
the second embodiment of the present invention;
Fig. 9 is a view for explaining two image reading modes;
Fig. 10 is a flow chart showing the processing executed when a color mixing amount
Kj is obtained in the image reading modes shown in Fig. 9;
Fig. 11 is a block diagram showing the arrangement of principal part according to
the embodiment of the present invention;
Fig. 12 is a block diagram showing the arrangement of a color mixing correction unit;
Fig. 13 is a view showing the arrangement of an image reading apparatus according
to the embodiment of the present invention;
Fig. 14 is a view for explaining another example of two image reading modes;
Fig. 15 is a flow chart showing the processing executed when a color mixing amount
Kj is obtained in the image reading modes shown in Fig. 14;
Fig. 16 is a block diagram showing another arrangement of a CCD linear image sensor;
Fig. 17 is a view showing the arrangement of an image reading apparatus using the
CCD linear image sensor shown in Fig. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The preferred embodiments of the present invention will be described in detail hereinafter
with reference to the accompanying drawings.
(First Embodiment)
[0028] Fig. 4 is a view showing the arrangement of a CCD linear image sensor used in a color
image reading apparatus according to the first embodiment of the present invention,
and Fig. 5 is a view showing the arrangement of a color mixing correction circuit
for correcting color mixing in the linear image sensor shown in Fig. 4.
[0029] Referring to Fig. 4, components denoted by reference numeral 301 to 309 are the same
as those in Fig. 3. Unlike in Fig. 3, the light-receiving units 301, 302, and 303
respectively having R (red), G (green), and B (blue) color-separation filters in Fig.
4 are arranged adjacent to each other. When the light-receiving units 301 to 303 read
an image, a charge stored in the R light-receiving unit 301 is directly transferred
to CCD transfer units 304 and 305, and a charge stored in the B light-receiving unit
303 is transferred to CCD transfer units 308 and 309, while a charge stored in the
G light-receiving unit 302 is temporarily transferred to the B light-receiving unit,
and is then transferred to CCD transfer units 308 and 309.
[0030] Fig. 6 shows the model of transfer of charges stored in the G and B light-receiving
units. In Fig. 6, reference numeral 401 denotes one pixel of the G light-receiving
unit; and 402, one pixel of the B light-receiving unit. When the image reading operation
is started from state A:start in Fig. 6, the light-receiving units 401 and 402 scan
on an original image in the direction of an arrow in state B. When these units scan
for about one pixel, a charge E
B stored in the B light-receiving unit 402 is transferred to a B CCD transfer unit
404 (state C in Fig. 6).
[0031] Let ΔT₁ be the charge transfer time from the light-receiving unit to the CCD transfer
unit. Then, the light-receiving unit continues the scanning operation and stores the
charge ΔE
B1 during the time ΔT₁. Therefore, the total charge amount, sigB, upon completion of
transfer of the charge stored in the B light-receiving unit is given by:

[0032] Then, as shown in state D, a charge E
G stored in the G light-receiving unit 401 is transferred to the B light-receiving
unit 402 from which the charge has already been transferred. Let ΔT₂ be the charge
transfer time from G light-receiving unit to the B light-receiving unit. Then, a charge
ΔE
B2 is stored in the B light-receiving unit during the time ΔT₂, and color mixing of
G and B (E
G + ΔE
B2) occurs. Furthermore, the charge transferred to the B light-receiving unit is transferred
to a G CCD transfer unit 403 (state E). In this case, since the B light-receiving
unit stores a charge ΔE
B1 during the charge transfer time ΔT₁ from the light-receiving unit to the CCD transfer
unit in the same manner as described above, the total charge amount, sigG, stored
until the transfer of the charge of the G light-receiving unit to the G CCD transfer
unit is completed is given by:

The amount of the B signal mixed in the G signal E
G is ΔE
B2 + ΔE
B1.
[0033] Since the same description as B applies to the R light-receiving unit from the arrangement
shown in Fig. 4, from equation (1), the total charge amount, sigR, of the R light-receiving
unit is given by:

[0034] The charges given by equations (1), (2), and (3) sequentially move in the CCD transfer
units, and are output to circuits shown in Fig. 5. The operation of this embodiment
will be described below with reference to Fig. 5.
[0035] The charges (to be referred to as analog image signals hereinafter) output from the
CCD transfer units are amplified to a predetermined level by amplifier circuits (not
shown), and are sampled/held by sample/hold (S/H) circuits 101, 102, and 103. The
outputs from the S/H circuits 101, 102, and 103 are converted into digital signals
by A/D converters 104, 105, and 106.
[0036] Let Rn (= sigR), Gn (= sigG), and Bn (= sigB) respectively be R, G, and B reading
signals, which are output from the A/D converters 104, 105, and 106 and correspond
to an n-th scan line of the line sensor. Then, Bn is multiplied with a color mixing
correction coefficient C0 (to be described later) by a multiplier 108, and an adder
109 subtracts C0•Bn from Gn, thus obtaining G'n. That is,

[0037] The above-mentioned signals Rn, G'n, and Bn are also obtained upon reading of a standard
white level prior to reading of an original image (these reading signals will be referred
to as shading data hereinafter). The shading data are stored in a shading data memory
113 comprising R, G, and B RAMs 110, 111, and 112.
[0038] Upon reading of an original image, R, G, and B image signals are subjected to shading
correction by shading correction circuits 114, 115, and 116 (i.e., a shading correction
circuit 117) as in a conventional image reading apparatus.
[0039] The determination of the color mixing correction coefficient C0 will be explained
below with reference to Fig. 6 again.
[0040] In Fig. 6, let T be the time required for the B light-receiving unit 402 to store
the charge E
B for one pixel (the B light-receiving unit obtains the charge E
B for the storage time T). In state C in Fig. 6, since the light-receiving unit requires
the time ΔT₁ for transferring the charge to the CCD transfer unit, the charge amount,
ΔE
B1, stored in the B light-receiving unit during the time ΔT1 is:

Therefore, from equation (1), the total charge amount sigB upon completion of the
transfer of the charge stored in the B light-receiving unit is given by:

The same applies to the R light-receiving unit, and from equation (3), the total charge
amount sigR is given by:

[0041] As for the G light-receiving unit, as shown in state D in Fig. 6, since the transfer
time of the charge E
G of the G light-receiving unit to the B light-receiving unit is ΔT₂, the charge amount
ΔE
B2 mixed in the charge E
G from the B light-receiving unit during the time ΔT₂ is:

Furthermore, since the charge ΔE
b1 stored (mixed) upon transfer of the charge of the B light-receiving unit to the G
CCD transfer unit 403 is ΔT₁•E
B/T from equation (5), the total charge amount sigG stored until the transfer of the
charge of the G light-receiving unit to the G CCD transfer unit is completed is given,
from equation (2), by:

Consequently, the charge amount of the B light-receiving unit mixed in the charge
E
G is (ΔT₂ + ΔT₁)E
B/T, and if this amount is assumed to be C times the total charge amount sigB of the
B light-receiving unit, from equation (6), we have:

and

and the stored charge amount E
G of the G light-receiving unit is obtained by subtracting the product of the B total
charge amount sigB and C from the G total charge amount sigG. That is,

[0042] In Fig. 5, since the B signal Bn is multiplied with C0 by the multiplier 108, and
the product is added by the adder 109, if the coefficient C0 is represented by -C,
C0 is given by:

[0043] As described above, the signal from the G light-receiving unit is subjected to shading
correction after subtraction of the signal from the B light-receiving unit weighted
with the correction coefficient C0 from the G signal is performed for shading data
and image reading data, thus realizing color mixing correction.
[0044] Note that the charges ΔE
B1 and ΔE
R1 are also stored in the B and R light-receiving units upon charge transfer. However,
since the charges of the same colors are stored upon reading of shading data, these
charges do not influence shading-corrected signals. Therefore, as can be seen from
the above description, the correction circuit need only be prepared for the G light-receiving
unit (a color for which a charge is transferred via a light-receiving unit of another
color).
(Second Embodiment)
[0045] In the first embodiment, the charge amount (ΔE
B2 + ΔE
B1) of the B light-receiving unit mixed in the charge E
G stored in the G light-receiving unit is determined based on the storage time ratio
(ΔT₂ + ΔT₁)/T of the charge EB stored in the B light-receiving unit from equation
(9). However, in practice, since charge transfer is performed in a finite time ΔT
at the boundary between the sampling periods of two pixels, strictly speaking, the
mixed charge amount stored at this time is determined by the charge amount of the
two pixels sandwiching the charge transfer time therebetween.
[0046] This determination method will be explained below with reference to Figs. 7 and 8.
[0047] Fig. 7 shows the time change in incident light amount when the B light-receiving
unit reads an original image. In Fig. 7, time is plotted along the abscissa, and the
incident light amount is plotted along the ordinate. In Fig. 7, the incident light
amount changes in correspondence with the reflectance of an original image, as indicated
by a curve shown in Fig. 7, and the stored charge amount is proportional to the product
(the hatched area in Fig. 7) of the incident light amount and the storage time.
[0048] Assuming that the sampling interval of an image is a period indicated by "← 1 pixel
→" in Fig. 7, charge transfer is performed during a finite time having the switching
timing of the sampling periods as the center. In particular, the charge of the B light-receiving
unit, which is mixed in the G light-receiving unit, is stored during the transfer
time (ΔT₂) from the G light-receiving unit to the B-light receiving unit and the transfer
time (ΔT₁) from the B light-receiving unit to the G CCD transfer unit, as shown in
Fig. 6.
[0049] At this time, the stored charge amount is expressed by a hatched portion ΔE
B in Fig. 7. Since this charge amount is stored during the time ΔT₂ and then during
the time ΔT₁, the stored charge amount during the time ΔT₂ can be approximated by
a charge E
Bn, and the charge amount during the time ΔT₁ can be approximated by a charge E
Bn+1 of the next pixel.
[0050] More specifically, equation (9) can be rewritten as:

[0051] Using sigBn and sigBn+1 of equation (6), the mixed charge amount (the second and
third terms of the right-hand side of equation (13)) is given by:

This is nothing but a sum of the product of the total charge amount sigBn of the B
light-receiving portion and a correction coefficient C1:

and the product of the total charge amount sigBn+1 of the next pixel of the B light-receiving
unit and a correction coefficient C2:

[0052] Fig. 8 shows the circuit arrangement for realizing this. In Fig. 8, line memories
501, 502, and 503 are used for attaining synchronization when the correction term
as a sum of the image signal delayed by one line and the image signal of the line
of interest of the B light-receiving unit is subtracted from the image signal of the
G light-receiving unit. Of these line memories, the R line memory 501 is not particularly
required here if it is realized by post-processing (not shown).
[0053] An image signal Bn delayed by one line by the line memory 503 and the image signal
Bn+1 of the next line are respectively multiplied with the correction coefficients
C1 and C2 given by equations (15) and (16) by multipliers 504 and 505, and the products
are added to each other by an adder 506. This correction term (given by equation (14))
is added to an image signal Gn delayed by one line by the adder 109 to obtain G'n.
(Third Embodiment)
[0054] In the first and second embodiments, the R, G, and B light-receiving units are arranged
adjacent to each other, as shown in Fig. 4. However, even when the light-receiving
units are separated from each other, as shown in Fig. 3, color mixing can be corrected
by the same correction method by increasing the number of line memories 501, 502,
and 503 as required, and synchronizing the read image positions of colors whose charges
are transferred via other charges and colors via which other charges are transferred.
[0055] As described above, according to this embodiment, the product of image data of the
light-receiving unit of a given color via which a stored charge is transferred, and
a correction coefficient is subtracted from image data, which is obtained by transferring
a stored charge to the CCD transfer unit via the light-receiving unit of the given
color, thereby correcting color mixing caused by transferring stored charges via another
color pixel.
(Fourth Embodiment)
[0056] The fourth embodiment of the present invention will be described below. In this embodiment,
the present invention is applied to an image processing apparatus. However, the present
invention is not limited to this, but may be applied to an image reader of, e.g.,
a copying machine.
[0057] As a CCD linear image sensor used in the image processing apparatus of this embodiment,
the sensor shown in Fig. 3 above can be used. Referring to Fig. 3, reference numeral
301 denotes an R light-receiving unit having an R color filter; 302, a G light-receiving
unit having a G color filter; 303, a B light-receiving unit having a B color filter;
304 and 305, ODD- and EVEN-pixel CCD transfer units for reading out charges stored
in the R light-receiving unit; 306 and 307, ODD- and EVEN-pixel CCD transfer units
for reading out charges stored in the G light-receiving unit; 308 and 309, ODD- and
EVEN-pixel CCD transfer units for reading out charges stored in the B light-receiving
unit; and 310 to 315, amplifiers for converting transferred charges into voltage signals,
and outputting the voltage signals. Since the CCD transfer units of this CCD linear
image sensor are not arranged between adjacent ones of the R, G, and B light-receiving
units, the R-G and G-B intervals shown in Fig. 3 can be decreased. Since charges stored
in the R and B light-receiving units can be transferred (shifted) to the corresponding
CCD transfer units without going through any light-receiving units of other colors,
no color mixing occurs. However, since a charge stored in the G light-receiving unit
must be transferred (shifted) to the corresponding CCD transfer units via the B light-receiving
unit, a charge generated by the B light-receiving unit is added to this charge, thus
causing color mixing (B → G color mixing in this case).
[0058] In this embodiment, when the CCD linear image sensor shown in Fig. 3 is used, a standard
original (an original with a given density) is read in modes A and B shown in Fig.
9, and the B → G color mixing amount is calculated based on the reading signal obtained
in these modes. Then, a color mixing correction coefficient is calculated from the
calculated color mixing amount, thereby correcting color mixing. As shown in Fig.
9, in the mode A, the light-receiving/charge storage period of the light-receiving
unit (to be referred to as a "light-receiving/storage period" hereinafter) and the
charge read-out time of the CCD transfer unit are respectively set to be a time T.
In the mode B, the light-receiving/storage period and the charge read-out time are
set to be twice (2T) the time in the mode A. On the other hand, the charge transfer
(shift) time from the light-receiving unit to the CCD transfer unit is set to be a
time ΔT in both the modes A and B. Therefore, signals G obtained in the modes A and
B include the following signal components:


where
- GAj
- : a signal G obtained in the mode A
- GBj
- : a signal G obtained in the mode B
- gAj
- :a signal obtained by removing the color mixing component from GAj
- gBj
- : a signal obtained by removing the color mixing component from GBj
- Kj
- : the color mixing amount from B to G
- j
- : the pixel number
From the relationship of the light-receiving/storage periods, g
Aj and g
Bj hold an equation below:

Therefore, from equations (17) to (19), an equation below is obtained:

[0059] Fig. 10 is a flow chart showing the processing when this color mixing amount K
j is obtained. In step S1, a standard original is read in the mode A. In step S2, the
same standard original is read in the mode B. Thereafter, the calculation of equation
(20) is made in step S3 to obtain the color mixing amount K
j. The above-mentioned processing can be executed before an actual image reading operation.
By matching parameters in the normal reading operation with those in the mode A, a
B → G color mixing ratio α
j is obtained by an equation below. Based on this color mixing ratio α
j, color mixing correction is performed in the actual original reading operation.

where B
Aj: a signal B obtained in the mode A
[0060] Fig. 11 is a block diagram showing principal part according to the present invention
in this embodiment.
[0061] Referring to Fig. 11, reference numeral 401 denotes an input unit comprising the
CCD linear image sensor shown in Fig. 3. The input unit 401 separates light reflected
by an original into three, i.e., R, G, and B, color components, and outputs electrical
signals corresponding to these color components. R, G, and B analog signals output
from the input unit 401 are sampled and held by S/H circuits 402, 403, and 404, and
are then A/D-converted by A/D converters 405, 406, and 407 to obtain 8-bit R, G, and
B digital signals. When a conventional CCD linear image sensor shown in Fig. 2 is
used, for example, A/D-converted signals R and G must be delayed by predetermined
periods of time using delay memories so as to correct CCD spatial shifts of the R,
G, and B signals. However, this embodiment does not require such processing since
almost no spatial shift of the CCD occurs. Reference numeral 408 denotes a color mixing
correction unit unique to this embodiment, which unit performs the above-mentioned
color mixing correction to the A/D-converted signals. The arrangement of the unit
408 will be described later. Reference numeral 409 denotes a shading unit for performing
correction to the signals subjected to color mixing correction in accordance with
the shading characteristics of the input unit 401.
[0062] Reference numeral 410 denotes a CPU comprising, e.g., a one-chip microcomputer. The
CPU 410 controls the operation of the entire apparatus of this embodiment on the basis
of programs stored in its internal ROM. Also, the CPU 410 executes processing for
calculating the color mixing ratio a
j given by equation (21) using data in the respective modes stored in a RAM 412. Reference
numeral 411 denotes an operation unit comprising an input section which consists of
a keyboard, a touch panel, and the like, and can designate the above-mentioned test
mode, and a display section consisting of an LCD, indicators, and the like. The operation
unit 411 supplies an operator's instruction to the CPU 410, and displays information
from the CPU 410, e.g., the operation state and the operation condition of the apparatus
of this embodiment.
[0063] Fig. 12 is a block diagram showing the arrangement of the color mixing correction
unit 408.
[0064] Referring to Fig. 12, reference numerals 901 to 903 denote delay circuits for respectively
delaying R, G, and B image signals by 1H (1 line). Reference numeral 904 denotes a
color mixing ratio memory for sequentially outputting the B → G color mixing ratios
α
j stored by the CPU 410 as the color mixing correction coefficients α
j corresponding to pixels in synchronism with the image signals. Note that a part of
the RAM 412 or the entire RAM 412 may be used as the color mixing ratio memory 904
for storing the color mixing ratios α
j and pixels in correspondence with each other.
[0065] Reference numeral 905 denotes an adder for adding a signal B input to the 1H delay
circuit 903 to a signal B output from the delay circuit 903. Reference numeral 906
denotes a divider for dividing the output from the adder 905 by 2. Reference numeral
907 denotes a multiplier which multiplies the output, B
Aj, from the divider 906 with the color mixing correction coefficient α
j output from the color mixing ratio memory 904, and outputs the B → G color mixing
amount K
j. Reference numeral 908 denotes a subtracter which subtracts the output (B → G color
mixing amount K
j) from the multiplier 907 from a signal G
Aj delayed by the 1H delay circuit 902, and outputs a signal G'(g
Aj) subjected to color mixing correction.
[0066] Note that the average value of the signals B before and after the 1H delay circuit
903 is used so as to interpolate B → G color mixing between an n-th line signal B
and the next (n+1)-th line signal B since the B → G color mixing occurs not in the
charge storage operation but in the charge transfer (shift) operation. This interpolation
allows accurate detection of the color mixing amount K
j, thus attaining color mixing correction with high precision.
[0067] Fig. 13 is a view showing the arrangement of the image reading apparatus of this
embodiment. The arrangement shown in Fig. 13 is substantially the same as that shown
in Fig. 1, except that a standard original 702 is placed on a standard original reader
701. The color mixing ratio α
j and the color mixing amount K
j can be measured by reading this standard original 701 in the modes A and B shown
in Fig. 9. Note that the measurement of K
j and α
j may be performed every image reading operation, or may be performed at predetermined
intervals set by the operation unit 411 or when a special instruction is input from
the operation unit 411. When the standard original 702 is placed on the standard original
reader 701, the environment upon detection of the color mixing amount K
j can be maintained constant, and an accurate color mixing amount K
j can always be detected.
(Fifth Embodiment)
[0068] The method of obtaining the color mixing amount K
j is not limited to that shown in Figs. 9 and 10. Figs. 14 and 15 show another method
of obtaining the color mixing amount K
j.
[0069] As shown in Fig. 14, the charge transfer period in the mode A (normal image reading
mode) is set to be a time ΔT, while in the mode C, the charge transfer period is set
to be twice (2•ΔT) that in the mode A. On the other hand, the same light-receiving/storage
period is set in both the modes A and C. Therefore, signals G obtained in the modes
A and C include the following components:


where G
Cj: a signal G obtained in the mode C
[0070] Since equation (24) below holds, the color mixing amount K
j is given by equation (25):


[0071] Fig. 15 is a flow chart showing the processing when the color mixing amount K
j is obtained. In step S11, a standard original is read in the mode A. In step S12,
the standard original is read in the mode C. Thereafter, equation (25) is calculated
in step S13 to obtain the color mixing amount K
j. In this manner, the calculation of the color mixing ratio α
j and color mixing correction upon image reading can be attained by the same method
and procedures as the above-mentioned method and procedures.
[0072] As described above, according to this embodiment, in the image reading apparatus
using the intra-pixel transfer type CCD linear image sensor, the color mixing amount
K
j and the color mixing ratio α
j representing color mixing are obtained, and the color mixing is corrected by signal
processing, thus obtaining an image free from color mixing.
(Sixth Embodiment)
[0073] The arrangement of the CCD linear image sensor is not limited to that shown in Fig.
3. Fig. 16 is a block diagram showing another arrangement of the sensor. The difference
in the sensor shown in Fig. 16 from that shown in Fig. 3 is that a charge of an R
light-receiving unit 501 is transferred via a B light-receiving unit 503, and a charge
of a G light-receiving unit 502 is transferred without going through any other light-receiving
units.
[0074] More specifically, the present invention is not limited to any specific disposition
order or intra-pixel transfer order of the R, G, and B light-receiving units.
[0075] Fig. 17 shows the arrangement of an image reading apparatus using the CCD linear
image sensor shown in Fig. 16. The difference in the arrangement shown in Fig. 18
from that shown in Fig. 13 is that a blue standard original 1101 is placed as a standard
original with a given density on the standard original reader 701. In Fig. 17, when
the blue standard original 1101 is read by the CCD 201, almost no charges are generated
by the R light-receiving unit 501. However, since charges are transferred to the CCD
transfer units 506 and 507 via the B light-receiving unit 503, B → R color mixing
occurs. Therefore, from signals R
j, G
j, and B
j (j is the pixel number) obtained when the blue standard original by the CCD 201,
the color mixing ratio α
j is given by:

[0076] As described above, when the blue standard original 1101 is used, two modes need
not be prepared, and the color mixing ratio α
j can be obtained by a simple arrangement and calculations. Although a detailed description
will be omitted, color mixing correction upon image reading can be attained by the
same method and procedures as the above-mentioned method and procedures.
[0077] Furthermore, this embodiment can be applied to all image processing apparatuses which
use intra-pixel transfer type CCD linear image sensors, which transfer a charge of
a light-receiving unit of a given color (first color component) via the second light-receiving
unit.
[0078] In the above embodiments, the color mixing ratio α
j is calculated in units of pixel numbers j. However, the present invention is not
limited to this. For example, only one color mixing ratio a
j may be obtained based on the average of all the pixels as long as color mixing caused
by intra-pixel transfer can be corrected.
[0079] The present invention may be applied to either a system constituted by a plurality
of apparatuses or an apparatus consisting of a single device.
[0080] The present invention may be applied to a case wherein the invention is attained
by supplying a program to the system or apparatus.
[0081] The present invention is not limited to the above embodiments and various changes
and modifications can be made within the spirit and scope of the present invention.
Therefore, to apprise the public of the scope of the present invention the following
claims are made.
1. An image pickup apparatus for reading a color image by irradiating light onto an object,
and photoelectrically converting light from the object, characterized by comprising:
a linear image sensor which comprises a plurality of light-receiving portions corresponding
to light components of a plurality of colors, and transfer units which are arranged
on two sides of said plurality of light-receiving portions and transfer charges from
said light-receiving portions, a charge stored in the light-receiving portion of at
least one color being transferred to the transfer unit via the light-receiving portion
of another color; and
calculation means for performing a calculation of the charge transferred via the
light-receiving portion of the other color.
2. The apparatus according to claim 1, wherein said calculation means adds a value obtained
by multiplying a charge amount stored in the light-receiving portion of the other
color with a correction coefficient.
3. The apparatus according to claim 1, further comprising normalization means for normalizing
with respect to standard white, and wherein the multiplication of the correction coefficient
and the addition of the charge multiplied with the correction coefficient are performed
prior to the normalization operation by said normalization means.
4. The apparatus according to claim 3, wherein the normalization operation by said normalization
means includes a shading correction.
5. The apparatus according to claim 1, wherein the correction coefficient is a constant
corresponding to a transfer time of the charge from the light-receiving portion to
the transfer unit, and a charge storage time.
6. The apparatus according to claim 1, further comprising a memory for at least one line,
and wherein the charge of the light-receiving portion via which the charge is transferred
includes a total of charges of two pixels before and after charge transfer, and
the correction coefficient includes at least two different constants respectively
corresponding to the charges of the two pixels.
7. The apparatus according to claim 5, wherein the correction coefficient is given by
-(ΔT₂ + ΔT₁)/(T + ΔT₁) where ΔT₂ is the time required for transferring the charge
via the light-receiving portion of the other color, ΔT₁ is the time required for transferring
the charge from the light-receiving portion of the other color to the transfer unit,
and T is the charge storage time.
8. The apparatus according to claim 6, wherein the correction coefficients associated
with the charges of the two pixels are respectively given by -ΔT₂/(T + ΔT₁) and -ΔT₁/(T
+ ΔT₁) where ΔT₂ is the time required for transferring the charge via the light-receiving
portion of the other color, ΔT₁ is the time required for transferring the charge from
the light-receiving portion of the other color to the transfer unit, and T is the
charge storage time.
9. An image reading method for reading a color image by irradiating light onto an object,
and photoelectrically converting light from the object, characterized by comprising
the steps of:
preparing a linear image sensor which comprises a plurality of light-receiving
portions corresponding to light components of a plurality of colors, and transfer
units which are arranged on two sides of said plurality of light-receiving portions
and transfer charges from said light-receiving portions, a charge stored in the light-receiving
portion of at least one color being transferred to the transfer unit via the light-receiving
portion of another color; and
performing a calculation of the charge transferred via the light-receiving portion
of the other color.
10. The method according to claim 9, wherein the calculation includes an addition of a
value obtained by multiplying a charge amount stored in the light-receiving portion
of the other color with a correction coefficient.
11. The method according to claim 9, further comprising the step of normalization with
respect to standard white, and wherein the multiplication of the correction coefficient
and the addition of the charge multiplied with the correction coefficient are performed
prior to the step of normalization.
12. The method according to claim 11, wherein the step of normalization includes a shading
correction.
13. The method according to claim 9, wherein the correction coefficient is a constant
corresponding to a transfer time of the charge from the light-receiving portion to
the transfer unit, and a charge storage time.
14. The method according to claim 9, further comprising the step of preparing a memory
for at least one line, and wherein the charge of the light-receiving portion via which
the charge is transferred includes a total of charges of two pixels before and after
charge transfer, and
the correction coefficient includes at least two different constants respectively
corresponding to the charges of the two pixels.
15. The method according to claim 13, wherein the correction coefficient is given by -(ΔT₂
+ ΔT₁)/(T + ΔT₁) where ΔT₂ is the time required for transferring the charge via the
light-receiving portion of the other color, ΔT₁ is the time required for transferring
the charge from the light-receiving portion of the other color to the transfer unit,
and T is the charge storage time.
16. The method according to claim 14, wherein the correction coefficients associated with
the charges of the two pixels are respectively given by -ΔT₂/(T + ΔT₁) and -ΔT₁/(T
+ ΔT₁) where ΔT₂ is the time required for transferring the charge via the light-receiving
portion of the other color, ΔT₁ is the time required for transferring the charge from
the light-receiving portion of the other color to the transfer unit, and T is the
charge storage time.
17. An image pickup apparatus characterized by comprising:
a first light-receiving sensor;
a second light-receiving sensor;
transfer means, arranged on a side near said second light-receiving sensor and
opposite to said first light-receiving sensor, for reading out charges of said first
and second light-receiving sensors;
control means for reading out a charge signal of said second light-receiving sensor
via said transfer means, and for transferring a charge signal of said first light-receiving
sensor toward said transfer means via said second light-receiving sensor, and then
reading out the charge signal via said transfer means; and
calculation means for performing a calculation of the signals of the first and
second light-receiving sensors read out via said transfer means.
18. The apparatus according to claim 17, wherein sensitivity of said second light-receiving
sensor is lower than sensitivity of said first light-receiving sensor.
19. The apparatus according to claim 17, wherein said first light-receiving sensor receives
a first color, and said second light-receiving sensor receives a second color.
20. The apparatus according to claim 19, wherein the second color is a blue color.
21. An image processing apparatus characterized by comprising:
reading means for reading a color image by an intra-pixel transfer method;
acquisition means for acquiring color mixing information between different color
signals from signals obtained by reading a standard portion by driving said reading
means in at least two different modes; and
correction means for correcting color mixing of image data read by said reading
means on the basis of the color mixing information acquired by said acquisition means.
22. The apparatus according to claim 21, wherein the standard portion is an original having
a predetermined density.
23. The apparatus according to claim 21, wherein said reading means comprises a light-receiving
unit for receiving light reflected by an original and storing a charge, and a transfer
unit for transferring the charge stored in said light-receiving unit.
24. The apparatus according to claim 23, wherein one of the modes is a normal image reading
mode, and the other mode is a mode in which a light-receiving time of said light-receiving
unit is a predetermined multiple of a light-receiving time in the normal image reading
mode.
25. The apparatus according to claim 23, wherein one of the modes is a normal image reading
mode, and the other mode is a mode in which a stored charge transfer time from said
light-receiving unit to said transfer unit is a predetermined multiple of a stored
charge transfer time in the normal image reading mode.
26. The apparatus according to claim 21, wherein said correction means removes a mixed
second color component from a first color component signal using an average value
of two lines of the second color component signals.
27. An image processing apparatus characterized by comprising:
reading means for reading a color image by an intra-pixel transfer method;
acquisition means for acquiring color mixing information from a first color component
to a second color component signal on the basis of a signal obtained by reading a
standard portion by said reading means; and
correction means for correcting color mixing of image data read by said reading
means on the basis of the color mixing information acquired by said acquisition means.
28. The apparatus according to claim 27, wherein the standard portion is an original of
the first color component.
29. An image processing method characterized by comprising:
the acquisition step of acquiring color mixing information between different color
signals from signals obtained by reading a standard portion by driving reading means
for reading a color image by an intra-pixel transfer method in at least two different
modes; and
the correction step of correcting color mixing of image data read by said reading
means on the basis of the color mixing information acquired in the acquisition step.
30. An image processing method characterized by comprising:
the acquisition step of acquiring color mixing information from a first color component
to a second color component signal on the basis of a signal obtained by reading a
standard portion by reading means for reading a color image by an intra-pixel transfer
method; and
the correction step of correcting color mixing of image data read by said reading
means on the basis of the color mixing information acquired in the acquisition step.
31. An image sensor for generating color component signals from a color image including
charge storage means for receiving light from the color image in which the outputs
relating to two color components of the color image are transferred over the same
path.